The present invention relates to the art of computer driven printers, particularly, color inkjet printers. Printers of this type have a printhead carriage which is mounted for reciprocal movement on the printer in a direction orthogonal to the direction of movement of the paper or other medium on which printing is to take place through the printer. The printer carriage of a color printer typically has four or more removable thermal ink jet printheads mounted thereon. Each of the printheads contains or is attached to a supply of ink and occasionally it is necessary to prime one or more printheads by creating a pressure differential to force ink to flow through the ink delivery orifices.
Printhead priming has previously been done by positioning a compliant seal around the nozzle plate of the printhead after the printhead carriage has been parked at a service station. In these systems, ink is drawn through the printhead nozzles by applying a negative pressure to the outside of the nozzle plates of the printheads to suck ink through the orifices. The source of the negative air pressure differential has been, among others, a collapsing air bellows or a remote pump connected by a fluid conduit. In these systems, the pressure is maintained by pressing a compliant cap against the surface surrounding the nozzles to create a chamber closed to the atmosphere but connected to the pressure source. The use of negative pressure to prime a printhead can have several disadvantages such as ink foaming, excessive waste ink and lack of precise control over the priming operation. Accordingly a system for printhead priming is required which does not rely upon negative pressure priming and by which a printhead can be primed in a controlled manner with minimal risk of system damage.